As Syria's fragmentation gathers pace and the demise of the regime apparently inches ever closer, competition between outside powers backing one side or the other is heating up, and proxy wars over the country's future are intensifying.

The latest example is the attempt by al-Qaeda to put its stamp publicly on the Nusra Front in Syria and encourage it to push for an Islamic state there, while its more moderate or secular partners in the common drive to oust the regime are committed to democracy.

It's a reminder that one aspect of the complex Syrian imbroglio is a proxy struggle between the US-led western world and al-Qaeda international.

Its leader, Ayman al-Zawahiri, the man who succeeded Osama Bin Laden, on Sunday urged jihadis in Syria to strive for an Islamic state that would be a foundation-stone for a wider regional caliphate.

That was followed two days later by al-Qaeda in Iraq announcing that the Nusra Front was one of its branches, and that the two were merging into a single Islamic State of Iraq and al-Sham (the Levant).

The US is reported to be involved in helping train elements of the Free Syrian Army

The Nusra Front, jockeying for position in the motley array of Syrian opposition forces and trying to win hearts and minds on the ground, clearly saw this as a potential kiss of death.

It swiftly turned down the public merger - though it was obliged to acknowledge its origins by pledging allegiance to Zawahiri, while insisting that that would change nothing.

Why this sudden flurry of public statements and display of disarray from the jihadis?

Western support

Over the past few months the Americans - without being obliged to announce any policy changes involving military commitments - have apparently tipped the wink to their regional allies, mainly Qatar, Turkey and Saudi Arabia, to step up the quantity and quality of arms supplies to the rebels.

At the same time, the Americans are reported to be involved in helping train supposedly moderate Free Syrian Army (FSA) elements in Jordan and sending them across the border into southern Syria, where the rebels, enjoying better anti-air and anti-armour weapons than before, have begun to make gains that are being compared to their advances in the far north.

With western support being made contingent on loyalty to the FSA and the opposition National Coalition, this has clearly put pressure on the Nusra Front and other jihadi groups.

Many of their followers are believed to have joined up opportunistically because the front had more resources and experience than the other groups.

With that trend now apparently starting to reverse and more resources being routed through the "moderate" groups, al-Qaeda may have judged it timely to remind the jihadists where their loyalties and objectives lie, lest they be lured away.

Knowing that the west is nervous about providing the Free Syrian Army and other "mainstream" rebel groups with serious, balance-tilting weaponry for fear that it may fall into the hands of the radicals, al-Qaeda may have decided deliberately to contaminate the entire opposition by association, and deter western arms to the moderates, in order to preserve the jihadis' ascendancy on the ground.

The nascent struggle between radicals and others in the opposition is bound to become more acute as regime change moves closer to reality, and if unresolved, will intensify further after it happens, possibly for a long time.

Regional repercussions

The outcome of that struggle will be crucial in determining the future of a vital core part of the region.

If the jihadis manage to retain their vanguard position in a new Syria, it is not hard to imagine the emergence of an informal - possibly even formal - union between Sunni parts of western Iraq and a Sunni-dominated Syria, as the region slides into a kind of sectarian and ethnic balkanisation whose fault-lines are already visible.

Russian and Iranian support for Bashar al-Assad is holding up

The survival of the Assad regime, or its transition into something retaining many of its pluralistic traits and structures, is the only serious obstacle to that process.

Which is one reason why the Americans and their allies are reluctant to push too hard in the other proxy struggle they are waging in Syria - against Iran and its allies, Hezbollah and the Damascus regime itself.

The dilemma the Americans face - and which they will be trying to resolve in a series of meetings between President Barack Obama and Middle East allies in the coming weeks - is how to back the rebels enough to induce the stubborn regime to negotiate a controlled transition, but not enough to trigger an abrupt regime collapse which might allow the radicals to take over.

It may be impossible to get that balance right. The inner core of the regime might not opt out until collapse is already there.

Provoking Israel?

In the meantime, diplomats say the Americans and their allies are encouraging the FSA rebels to take control of as much border terrain as they can, to try to contain the regional repercussions.

One fear is that as it becomes more desperate, the regime might try to lash out and provoke Israel in order to rally domestic and regional support. So a lot of the focus has been to seal off that possibility by creating a rebel-controlled buffer zone on the Syrian side of the Israeli-occupied Golan Heights.

Diplomats say Israel has been quietly co-operating, treating FSA wounded who are left by the ceasefire line and taken to a special field hospital in the Golan, with serious cases transferred to hospitals inside Israel.

In Lebanon, there are similar fears among Hezbollah's local adversaries that should the crisis deepen, it might try to trigger a cross-border escalation by provoking Israel in the south.

As pressure on Damascus mounts, and the rebels nudge forward with increasing if calibrated support from the west and its friends, the regime's allies are also rallying.

Russia and Iran are both believed to have renewed their commitment only to allow Bashar al-Assad to go as part of a balanced orderly transition that would retain much of the regime structure and state institutions.

Diplomats say Iran has already provided at least US $12.6bn in financial support to help the regime stay afloat and pay its followers.

Hezbollah's involvement

They say the Iranians are also funding, training and arming recently-formed local Popular Committee militias, separate from the shabiha militia network, seeing them as a structure they could continue to rely on if the regime should collapse and fall back on the Alawite-dominated areas on the north-west coast and its hinterland.

Iran's Hezbollah allies from Lebanon are also pitching in on the ground, fighting rebels around the important Shia shrine at Sayyida Zeinab on the southern edge of Damascus, and Shia villages in Homs province to the west.

Well-placed diplomats believe Hezbollah is also providing part of the regime's inner praetorian guard, as some of the big Alawite clans have become so alienated by the level of casualties they have suffered that their members are no longer regarded as fully reliable.

The Iraqi branch of Hezbollah, and other Iraqi Shia factions close to Iran, are also believed to have become involved to greater or lesser degree.

The Hezbollah Brigades in Iraq last week confirmed for the first time that one of its militants had been killed in Syria.

So both in Iraq and in Lebanon, Sunni and Shia activists and militants are displacing their internal struggle onto Syrian soil - with the clear risk that it could blow back into aggravated conflict at home.

Palestinian fighters are also reported to be involved on both sides, although their divisions are more to do with politics and patronage than sectarianism.

Despite denials, there have been persistent reports that militants from Hamas have been training Free Syrian Army fighters on the eastern side of Damascus. Hamas used to be based in the city and close to the regime, but has shifted allegiance to Qatar under the strain of the Syrian crisis and mounting Sunni-Shia polarisation in the region.

One of the regime's more dependable Palestinian allies, the Popular Front for the Liberation of Palestine-General Command headed by Ahmad Jibril (a former Syrian army officer), is reported to have joined the fray on the government side.

Trying to work with an opposition that is divided and far from in control of events on the ground, it is small wonder that the western powers themselves appear divided and hesitant as they ponder how to help achieve what they regard as an acceptable result from all this.

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